Abstract
The present study describes the mesoscale trough that often occurs over the Korean peninsula during the excursion of the Siberian High and investigates the mechanisms of its formation using both observations and a three-dimensional atmospheric numerical model. The mesoscale trough begins to form in the morning hours and shows a well-defined structure through-out the peninsula in the afternoon according to the case observed on 14-15 February 1986, during which the air temperature over the peninsula is higher than normal. It shows a weakening tendency in the early morning hours of the second day, but develops again during the daytime until it dissipates as the high pressure system over China moves eastward. A numerical simulation of this mesoscale trough produces fairly well the major observed features such as the temporal and spatial distribution of sea-level pressure. The results from various numerical experiments indicate that the mesoscale trough observed on 14-15 February 1986 forms as a result of the dynamical and thermal impacts of the mountain ranges on the Korean peninsula and the thermal contrast between the air over the peninsula and the neighboring seas under a relatively warmer winter day condition, with which surface sensible heat flux into the atmosphere during daytime is significantly larger over the peninsula than that over the neighboring seas. The trough over the northern half of the peninsula is mainly formed by the dynamical and thermal effects of the mountains in the northern peninsula, while the trough over the southern half of the peninsula is primarily formed by the thermal effects of the elevated area and the thermal contrast between air over the peninsula and the neighboring seas.
